Download The Urinary System

Human Anatomy & Physiology
The Urinary System
Functions of the Urinary System
 Elimination of waste products
 Nitrogenous wastes
 Toxins
 Drugs
Edited by Dr. Ryan Lambert-Bellacov
Slide
Functions of the Urinary System
 Regulate aspects of homeostasis
 Water balance
 Electrolytes
 Acid-base balance in the blood
 Blood pressure
 Red blood cell production
 Activation of vitamin D
Edited by Dr. Ryan Lambert-Bellacov
Slide
Organs of the Urinary system
 Kidneys
 Ureters
 Urinary bladder
 Urethra
Figure 15.1a
Slide 15.2
Location of the Kidneys
 Against the dorsal body wall
 At the level of T12 to L3
 The right kidney is slightly lower than
the left
 Attached to ureters, renal blood vessels,
and nerves at renal hilus
 Atop each kidney is an adrenal gland
Slide 15.3
Coverings of the Kidneys
 Renal capsule
 Surrounds each kidney
 Adipose capsule
 Surrounds the kidney
 Provides protection to the kidney
 Helps keep the kidney in its correct location
Slide 15.4
Regions of the Kidney
 Renal cortex –
outer region
 Renal medulla –
inside the cortex
 Renal pelvis –
inner collecting
tube
Figure 15.2b
Slide 15.5
Kidney Structures
 Medullary pyramids – triangular regions
of tissue in the medulla
 Renal columns – extensions of cortexlike material inward
 Calyces – cup-shaped structures that
funnel urine towards the renal pelvis
Slide 15.6
Blood Flow in the Kidneys
Figure 15.2c
Slide 15.7
Nephrons
 The structural and functional units of the
kidneys
 Responsible for forming urine
 Main structures of the nephrons
 Glomerulus
 Renal tubule
Slide 15.8
Glomerulus
 A specialized
capillary bed
 Attached to
arterioles on both
sides (maintains
high pressure)
 Large afferent
arteriole
 Narrow efferent
arteriole
Figure 15.3c
Slide
Glomerulus
 The glomerulus
sits within a
glomerular capsule
(the first part of the
renal tubule)
Figure 15.3c
Slide
Renal Tubule
 Glomerular
(Bowman’s)
capsule
 Proximal
convoluted
tubule
 Loop of Henle
 Distal
convoluted
tubule
Figure 15.3b
Slide
Types of Nephrons
 Cortical nephrons
 Located entirely in the cortex
 Includes most nephrons
Figure 15.3a
Slide
Types of Nephrons
 Juxtamedullary nephrons
 Found at the boundary of the cortex and
medulla
Figure 15.3a
Slide
Peritubular Capillaries
 Arise from efferent arteriole of the
glomerulus
 Normal, low pressure capillaries
 Attached to a venule
 Cling close to the renal tubule
 Reabsorb (reclaim) some substances
from collecting tubes
Slide
Urine Formation Processes
 Filtration
 Reabsorption
 Secretion
Figure 15.4
Slide
Filtration
 Nonselective passive process
 Water and solutes smaller than proteins
are forced through capillary walls
 Blood cells cannot pass out to the
capillaries
 Filtrate is collected in the glomerular
capsule and leaves via the renal tubule
Slide
Reabsorption
 The peritubular capillaries reabsorb several
materials
 Some water
 Glucose
 Amino acids
 Ions
 Some reabsorption is passive, most is active
 Most reabsorption occurs in the proximal
convoluted tubule
Slide
Materials Not Reabsorbed
 Nitrogenous waste products
 Urea
 Uric acid
 Creatinine
 Excess water
Edited by Dr. Ryan Lambert-Bellacov
Slide
Secretion – Reabsorption in
Reverse
 Some materials move from the
peritubular capillaries into the renal
tubules
 Hydrogen and potassium ions
 Creatinine
 Materials left in the renal tubule move
toward the ureter
Slide
Formation of Urine
Figure 15.5
Slide
Characteristics of Urine Used for
Medical Diagnosis
 Colored somewhat yellow due to the
pigment urochrome (from the
destruction of hemoglobin) and solutes
 Sterile
 Slightly aromatic
 Normal pH of around 6 (varies 4.5-8)
 Specific gravity of 1.001 to 1.035
Slide
Ureters
 Slender tubes attaching the kidney to
the bladder
 Continuous with the renal pelvis
 Enter the posterior aspect of the bladder
 Runs behind the peritoneum
 Peristalsis aids gravity in urine transport
Edited by Dr. Ryan Lambert-Bellacov
Slide
Urinary Bladder
 Smooth, collapsible, muscular sac
 Temporarily stores urine
Figure 15.6
Slide
Urinary Bladder
 Trigone – three openings
 Two from the ureters
 One to the urethrea
Figure 15.6
Slide
Urinary Bladder Wall
 Three layers of smooth muscle
(detrusor muscle)
 Mucosa made of transitional epithelium
 Walls are thick and folded in an empty
bladder
 Bladder can expand significantly without
increasing internal pressure
Slide
Urethra
 Thin-walled tube that carries urine from
the bladder to the outside of the body by
peristalsis
 Release of urine is controlled by two
sphincters
 Internal urethral sphincter (involuntary)
 External urethral sphincter (voluntary)
Slide
Urethra Gender Differences
 Length
 Females – 3–4 cm (1 inch)
 Males – 20 cm (8 inches)
 Location
 Females – along wall of the vagina
 Males – through the prostate and penis
Slide
Urethra Gender Differences
 Function
 Females – only carries urine
 Males – carries urine and is a passageway
for sperm cells
Slide
Micturition (Voiding)
 Both sphincter muscles must open to
allow voiding
 The internal urethral sphincter is relaxed
after stretching of the bladder
 Activation is from an impulse sent to the
spinal cord and then back via the pelvic
splanchnic nerves
 The external urethral sphincter must be
voluntarily relaxed
Slide
Maintaining Water Balance
 Normal amount of water in the human
body
 Young adult females – 50%
 Young adult males – 60%
 Babies – 75%
 Old age – 45%
 Water is necessary for many body
functions and levels must be maintained
Slide
Distribution of Body Fluid
 Intracellular fluid
(inside cells)
 Extracellular
fluid (outside
cells)
 Interstitial fluid
 Blood plasma
Figure 15.7
Slide
The Link Between Water and Salt
 Changes in electrolyte balance causes
water to move from one compartment to
another
 Alters blood volume and blood pressure
 Can impair the activity of cells
Slide
Maintaining Water Balance
 Water intake must equal water output
 Sources for water intake
 Ingested foods and fluids
 Water produced from metabolic processes
 Sources for water output
 Vaporization out of the lungs
 Lost in perspiration
 Leaves the body in the feces
 Urine production
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Maintaining Water Balance
 Dilute urine is produced if water intake
is excessive
 Less urine (concentrated) is produced if
large amounts of water are lost
 Proper concentrations of various
electrolytes must be present
Slide
Regulation of Water and Electrolyte
Reabsorption
 Regulation is primarily by hormones
 Antidiuretic hormone (ADH) prevents
excessive water loss in urine
 Aldosterone regulates sodium ion content of
extracellular fluid
 Triggered by the rennin-angiotensin
mechanism
 Cells in the kidneys and hypothalamus
are active monitors
Slide
Maintaining Water/Electrolyte Balance
Figure 15.9
Slide
Maintaining Acid-Base Balance in
Blood
 Blood pH must remain between 7.35
and 7.45 to maintain homeostasis
 Alkalosis – pH above 7.45
 Acidosis – pH below 7.35
 Most ions originate as byproducts of
cellular metabolism
Slide
Maintaining Acid-Base Balance in
Blood
 Most acid-base balance is maintained
by the kidneys
 Other acid-base controlling systems
 Blood buffers
 Respiration
Slide
Blood Buffers
 Molecules react to prevent dramatic
changes in hydrogen ion (H+)
concentrations
 Bind to H+ when pH drops
 Release H+ when pH rises
 Three major chemical buffer systems
 Bicarbonate buffer system
 Phosphate buffer system
 Protein buffer system
Slide
The Bicarbonate Buffer System
 Mixture of carbonic acid (H2CO3) and
sodium bicarbonate (NaHCO3)
 Bicarbonate ions (HCO3–) react with
strong acids to change them to weak
acids
 Carbonic acid dissociates in the presence
of a strong base to form a weak base and
water
Slide
Respiratory System Controls of
Acid-Base Balance
 Carbon dioxide in the blood is converted to
bicarbonate ion and transported in the
plasma
 Increases in hydrogen ion concentration
produces more carbonic acid
 Excess hydrogen ion can be blown off with
the release of carbon dioxide from the lungs
 Respiratory rate can rise and fall depending
on changing blood pH
Slide
Renal Mechanisms of Acid-Base
Balance
 Excrete bicarbonate ions if needed
 Conserve or generate new bicarbonate
ions if needed
 Urine pH varies from 4.5 to 8.0
Edited by Dr. Ryan Lambert-Bellacov
Slide
Developmental Aspects of the
Urinary System
 Functional kidneys are developed by
the third month
 Urinary system of a newborn
 Bladder is small
 Urine cannot be concentrated
Edited by Dr. Ryan Lambert-Bellacov
Slide
Developmental Aspects of the
Urinary System
 Control of the voluntary urethral
sphincter does not start until age 18
months
 Urinary infections are the only common
problems before old age
Edited by Dr. Ryan Lambert-Bellacov
Slide
Aging and the Urinary System
 There is a progressive decline in urinary
function
 The bladder shrinks with aging
 Urinary retention is common in males***
Edited by Dr. Ryan Lambert-Bellacov
Slide
Aging and the Urinary System
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